Multiple Threats Have Overlapping Impacts Across Ecological Levels in Freshwater Ecosystems

ABSTRACT Changes driven by climate change, biological invasion, land‐use change, pollution and overexploitation are decreasing the resilience of freshwater ecosystems worldwide. While the impact of these threats is widely recognised, a critical gap remains in systematically quantifying their relative effects across ecological levels, which is essential for linking impacts on multiple responses. This gap limits our ability to anticipate their potential additive effects and to establish baseline conditions for studies addressing interactive impacts on freshwater ecosystems. We conducted a meta‐analysis to assess the individual impacts of multiple threats on freshwater ecosystems at the population, community and ecosystem levels, integrating data across multiple response variables. Our findings revealed that individual threats show similar effects on specific ecological levels and key responses, leading to potential additive effects. Pollution and climate change consistently increased population‐level responses, whereas pollution and land‐use change increased productivity‐related processes at the ecosystem level. At the community level, biological invasion and land‐use change disrupted freshwater biodiversity, although all threats presented an overall decreasing effect on the related responses. Our results show that climate change, biological invasion, land‐use change, and pollution compromise freshwater ecosystems through similar magnitudes and directions of impact across ecological levels, revealing a consistent cross‐level convergence among threats. This cross‐level convergence provides an empirical basis for anticipating additive effects among threats, improving the design of target monitoring and management strategies for freshwater biodiversity.